A fixed spray sprinkler nozzle does not rotate during operation. Consequently, the arc of ground watered by such a nozzle is primarily determined by the configuration of the water discharge orifices in the nozzle. Such nozzles are typically made with different numbers and/or shapes of discharge orifices so that different nozzles will water different preset arcs. Thus, for a particular sprinkler to water a 90.degree. arc, a nozzle which has been built to water a 90.degree. arc will be installed on that sprinkler.
The practice of using different nozzles to water different arcs has various disadvantages. For example, the installer has to stock all of the different nozzles for the different arcs, which is obviously costly and inconvenient. Moreover, to adjust an existing sprinkler from one arc to another, the installer has to first remove the old nozzle and then install a new nozzle configured to water the desired arc. In addition to the labor involved in this process, the old nozzle is often just thrown away, thereby making this method of arc adjustment somewhat wasteful.
The art has recognized these deficiencies and has attempted to provide a "universal" fixed spray sprinkler nozzle, i.e. a single nozzle having an adjustable arc coverage. In nozzles in which the water discharge orifice comprises an elongated slot extending around the circumference of the nozzle, a rotatable flow controlling skirt abuts against the inside of the slot to control the open length of the slot. When the skirt fully covers the slot, no flow is allowed through the nozzle and the sprinkler is shut off. As the skirt is rotated to begin uncovering the slot, the arc coverage is progressively increased until the slot is fully open with the sprinkler watering its maximum arc. U.S. Pat. No. 682,590 to Greer shows an adjustable nozzle of this type.
Nozzles having a water discharge slot located at a constant axial height along the axis of the nozzle, as in Greer, are typically adjustable only between 0 and 180.degree.. Obviously, even if a slot is cut all the way around the circumference of the nozzle, the flow blocking skirt always blocks some portion of the slot. Thus, the slot typically extends only about halfway around the nozzle. Since the maximum arc coverage of this type of nozzle is limited to 180.degree. or so, it does not fulfill the need for a "universal" nozzle whose arc could be adjusted all the way up to 360.degree. if so desired.